Clinical trial data has shown that post-menopausal women with breast cancer who were treated using Aromasin demonstrated a significantly reduced risk of recurrence and increased disease-free survival than those treated with tamoxifen. With Aromasin's patent up in 2006, Pfizer [PFE] should now concentrate on marketing this product as a second-line treatment.
Results from a phase II, open-label, multicenter controlled clinical trial sponsored by Pfizer, which developed Aromasin (exemestane), were presented at the fourth European Breast Cancer Conference in Hamburg, Germany on March 18.
The trial investigated the efficacy of exemestane in 382 post-menopausal women with metastatic breast cancer who had failed previous tamoxifen therapy. It was shown that median survival in exemestane treated patients was 10.9 months compared to 6.7 months in tamoxifen treated patients. Of those treated with exemestane, 7.4% showed a complete response and 36.8% showed a partial response, compared with 2.6% and 26.6% respectively in those patients treated with tamoxifen.
Exemestane is an aromatase inhibitor that works by binding to the aromatase enzyme, which normally converts androgen into estrogen in post-menopausal women, thus restricting the supply of estrogen to tumors that are dependent on it.
Aromasin is currently approved for the second-line treatment of metastatic breast cancer in post-menopausal women. The drug was launched in the US, UK, Switzerland and Germany in 2000 by Pharmacia, and in Japan in 2002. In April 2003, Pfizer acquired Pharmacia, and Aromasin. Despite this, the drug is not one of Pfizer's best sellers.
The gold-standard treatment for post-menopausal women with metastatic breast cancer is tamoxifen therapy following primary treatment for the initial tumor. Although many women do respond to tamoxifen, others show no response and its efficacy appears to diminish after five years. There is the potential for exemestane to be used alongside tamoxifen, or even replace it.
However, Aromasin faces strong competition from AstraZeneca's [AZN.L] Arimidex (anastrozole), which is the leading aromatase inhibitor for the treatment of breast cancer, as well as Novartis's [NVS] Femara (letrozole). A further disadvantage faced by Aromasin is its patent expiry date of 2006, earlier than both Arimidex (2009) and Femara (2011). The results from this trial suggest Aromasin could be more effective than tamoxifen as a first-line treatment. However, because of patent expiry constraints, Pfizer should market Aromasin only as a second or even third-line treatment to increase uptake.